PHARMACOGNOSY : PHYSICAL METHODS OF EVALUATION OF CRUDE DRUGS

PHYSICAL METHODS OF EVALUATION OF CRUDE DRUGS

1. DETERMINATION OF MOISTURE CONTENT:

The moisture content can be determined by heating the drug in oven at 105°C to a constant weight. Toluene Distillation method is used for determining the Moisture content of drug those contains Volatile active constituents.

2. DETERMINATION OF VISCOSITY: METHOD BY USING OSTWALD VISCOMETER:

Procedure: Fill the Viscometer, Previously washed with chromic acid E and five times with distilled water with the liquid being examined through tube L to slightly above the mark G, using a long pipette to minimize wetting the tube above the mark. Place the tube vertically in water bath which temperature is maintained at the temperature at which viscosity is to be measured. When the temperature of liquid in tube attends, adjust the volume of liquid so that the bottom of the meniscus set at the mark G. Attach the rubber tube to E end of the tube and suck the liquid 5mm above the point E.

After releasing the suction, Measure the time required for the bottom of the meniscus to fall from the top edge of mark E to the top edge of mark F.

Kinematic Viscosity = Kt. (Unit is Sq.mm per second)

Dynamic Viscosity = KPt (Unit is Millipascal second Symbol – mPa S.)

Where, K is constant of instrument, which P determined by using Liquid of known viscosity.

t is time in second for the meniscus to fall from E to F.

P is weight per Ml of liquid in g/Cubic cm.

Viscosity can be measured by using other viscometers like Brookfield Viscometer, which is more accurate.

3. DETERMINATION OF MELTING POINT:

Pure chemicals and Photochemical are having sharp melting points. Crude drugs from animal and plant origin contain the mixed chemicals; they are described with certain range of melting points.

4. DETERMINATION OF ACID VALUES:

Definition: It is defined as the number which expresses in mg the amount of Potassium Hydroxide (KOH) necessary to neutralize the free acids presents in the 1g of the sample. Weight accurately 10g of sample and dissolve it in 50ml of a mixture of Ethanol 95% (25 ML) and Ether (25 ML) previously neutralized with 0.1M Potassium Hydroxide to Phenolphthalein solution. If required dissolve the sample by heating slowly and using reflex condense. To the above sample solution add 1ml of Phenolphthalein indicator and titrate with 0.1M Potassium Hydroxide solution up to the end point pink after shaking for half minute.

Acid value = 5.61n/w

Where n – ml of 0.1 M Potassium Hydroxide solution required.

w – Weight of sample in g.

5. DETERMINATION OF VALUE:

Definition: It is defined as the number of milligrams of Potassium Hydroxide required to saponify the Esters in the 1g of sample substance. It is calculated by subtracting the Saponification value from the Acid value of sample substance.

6. DETERMINATION OF SAPONIFICATION VALUE:

It is defined as the number of milligrams of Potassium Hydroxide required for neutralization of free acid and to saponify the esters present of 1g of sample.

Weight accurately 2g of sample and add it to 200ml glass flask fitted with reflex condenser. Add 25ml of 0.5 M Ethanolic potassium hydroxide and small quantity of pumice powder and boil for 30 min on water bath under reflux. Add 1ml Phenolphthalein solution and titrate immediately with 0.5 M hydrochloric acid (x). Take the blank reading by repeating the same procedure (y). Calculate the saponification values as:

Saponification value = 28.05 (y-x) / w

Where, w - Weight of substance in g.

7. DETERMINATION OF IODINE VALUES:

Iodine value is defined as the number which expresses in grams the quantity of halogen, calculated as iodine, which is absorbed by 100g of the substance under the described condition.

Add accurately weighed quantity of sample in dry 500ml Iodine flask, add 10ml of carbon tetrachloride and dissolve. Add 20 ml of Iodine Monochloride solution fix the stopper and allow it to stand for 30 minute between temperatures 15 to 25°C in dark place. Add 15ml of Potassium Iodide solution in cup top and carefully remove the stopper, rinse the stopper and side of the flask with 100ml of water, mix by shaking and titrate with 0.1 M sodium Thiosulphate solution using Starch solution as indicator towards the end of titration. Note the Burette reading (x) and repeat the same procedure for blank titration and record the Burette reading (y).

Iodine Value = 1.269 (y-x) / w

Where, w is weight of sample in g.

8. DETERMINATION OF ETHANOL SOLUBLE EXTRACTIVE:

Prepare coarse powder of air dried drug. Take 100ml of Ethanol (Specified Strength) in conical flask. Macerate 5g of powdered drug in above conical flask, close and conical flask for 24 hours. Shake the flask frequently during first 6 hours; allow it to stand for 18 hours. Filter rapidly taking precaution against loss of ethanol evaporate 25ml of the filtrate to dryness in a tared flat bottomed shallow dish. Dry at 105°C and weight it. Calculate the % of Ethanol soluble extractive with reference to the air dried drug.

9. DETERMINATION OF WATER SOLUBLE EXTRACTIVE:

Follow the procedure described under Ethanol Soluble Extractive. Use Chloroform water instead of ethanol.

10. DETERMINATION OF ASH FROM CRUDE VEGETABLE DRUGS:

Weight accurately 2 to 3g of air dried crude drug in a treated silica dish and incinerate at a temperature not exceeding 450°C until free from carbon. Cool the Silica dish and weight. If a carbon free ash can not be obtained. Exhaust the charred mass with hot water. Collect the residue on an ash less filter paper, until the ash in white or nearly white, add the filtrate evaporate to dryness and ignite at a temperature not exceeding 450°C. Calculate the % of ash with reference to the air dried drug.

11. DETERMINATION OF REFRACTIVE INDEX:

The instrument used to measure the refractive index if liquids are called refractometer. Refractive index is defined as the ratio of the sin of the angles of incidence and refraction.

n = Sin i

Sin r

Where, n is refractive index,

Sin i – Sine of angle of incidence and

Sin r – Sine of angle of refraction.

RI is useful for measurement of Molecular Formula. It is measured at 20°C ± 5°C temperature.

The Abbe refractometer is used for accurate measurements of RI. It consists of Abbe’s prism, Telescope, Compensation Prism and Sector.

Wash and dry the prisms, place few drops of liquids on surface of lower prism and close the prisms. Focus the eyepiece by sliding it up and down until cross hairs are in sharp focus. Turn the compensator until coloured fringes disappear. Rotate the indicator so that the borderline coincides with the intersection of the cross hairs. Note the reading. Repeat the same experiments for 2 to 3 times. Mean of these repeated readings gives the refractive index.